Pin grid array package

ABSTRACT

In a method of forming a protective cover of a pin grid array in which a semiconductor chip is mounted on an upper surface of a resin board having a plurality of contact pins on a lower surface thereof, the pin grid array is inserted in a recess of a lower mold so as to be at a level lower than an upper surface of the lower mold and to leave a space therearound, the lower mold having the recess for receiving the resin board, grooves, formed on a bottom of the recess, for receiving the contact pins, and projections, formed on a peripheral portion of the recess, for abutting against part of side surfaces of the resin board. An upper mold is then placed above the upper surface of the lower mold. Finally, a thermosetting resin is injected in a gap defined between the upper and lower molds, thereby performing transfer molding. A pin grid array manufactured by the above method is also disclosed.

This is a divisional application of U.S. Ser. No. 037,745, filed on Apr.13, 1987, now U.S. Pat. No. 4,822,550.

BACKGROUND OF THE INVENTION

2. Field of the Invention

The present invention relates to a method of forming a protective coverof a pin grid array (to be referred to as a PGA hereinafter) in which anIC chip is mounted on a resin board having contact pins on its lowersurface and which serves as an interchangeable memory of a microcomputeror the like.

2. Description of the Prior Art

When a PGA having an IC chip thereon is mounted in an apparatus and thenreplaced with another PGA, the function of the apparatus can be changedto another function. Therefore, the PGA is widely used to increase theapplication fields of the apparatus. As a circuit board of the PGA ofthis application, a ceramic board, resin board, or the like is used. Aceramic board has a good insulating property and thus has highreliability as a product. However, since a wiring pattern is formed onthe ceramic board by printing or baking, contraction occurs and it isdifficult to increase the number of wiring patterns and to miniaturize apattern. When the number of wirings is increased, the board size isinevitably increased, resulting in a high price.

A resin board has been recently used, in place of a ceramic board, asthe circuit board of a PGA. FIG. 1 shows an example of a resin boardwherein a frame 2 is attached to a resin board 1, and a potting resin 3is dropped in the frame 2, thereby molding an IC chip 4. The IC chip 4and a terminal pattern 5 printed on the resin board 1 are electricallyconnected through lead wires 6. Contact pins 7 extend from the lowersurface of the resin board 1. Stand pins 9 having steps for heightregulation extend from a peripheral portion of the lower surface of theresin board 1 in order to facilitate attachment/detachment with respectto a PGA socket 8. A PGA of this type enables micro-patterning at areasonable cost since the molded resin 3 is in tight contact with the ICchip 4 and a circuit pattern is formed on the resin board 1 by etching.However, its reliability is not satisfactory since the resin haswettability. More specifically, in resin molding by means of potting, amolded portion becomes porous and allows penetration of a moisture, andmoisture penetration from an interface A between the resin board 1 andthe molded potting resin 3 and from cut side surfaces B of the boardtypically occurs. In order to solve this humidity problem, a PGA asshown in FIG. 2 is conventionally known. In the PGA shown in FIG. 2, anIC chip 4 is mounted on a resin board 1 and molded by a resin 3, and anentire upper surface of the resultant structure is covered by a metalcap 10. Although the PGA of this type improves moisture penetration to acertain degree, it requires a special manufacturing step for coveringthe metal cap 10, and moisture still penetrates from a gap between themetal cap 10 and the resin board 1.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method of forminga protective cover of a PGA, from which the above-mentioned conventionaldrawbacks are eliminated, and a resin-molded PGA manufactured inaccordance with the same.

More specifically, it is a first object of the present invention toprovide a method of forming a protective cover of a pin grid array,comprising the steps of: mounting a pin grid array, in which a pluralityof contact pins extend from a lower surface thereof and which isobtained by mounting an IC chip on a resin board, on a lower mold havinga recess for receiving the resin board, escape holes for the contactpins, and projections for partially holding side surfaces of the resinboard, the escape holes and the projections being formed on a bottom ofthe recess; positioning an upper mold on the lower mold such that a gapis formed on the upper and the side surfaces of the pin grid array; andinjecting a thermosetting resin into a gap defined between the upper andlower molds, thereby performing transfer molding.

It is a second object of the present invention to, provide a pin gridarray in accordance with the above method, wherein upper and sidesurfaces of a resin board having an IC chip thereon are sealed with amolding resin.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a molding example of a conventionalPGA using a resin board;

FIG. 2 is a sectional view showing another molding example of aconventional PGA using a resin board;

FIG. 3 is a perspective view cf a resin-molded PGA manufacturedaccordance with a method of the present invention;

FIG. 4 is a sectional view of the PGA taken along the line 4--4 of FIG.3;

FIG. 5 is a bottom view of the PGA shown in FIG. 3;

FIG. 6 is a sectional view of the PGA before resin molding;

FIG. 7 is a perspective view showing upper and lower molds used in themethod of the present invention;

FIGS. 8A and 8B are views for explaining the manufacturing method of thepresent invention, in which FIG. 8A shows a state of the molds beforemolding and FIG. 8B shows a state of the molds after molding;

FIG. 9 is a perspective view of another lower mold used in the presentinvention;

FIG. 10 is a perspective view of another upper mold used in the presentinvention: and

FIG. 11 is a perspective view of a PGA whose protective cover is formedby using the upper mold shown in FIG. 10.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 3 shows an outer appearance of a resin-molded PGA manufactured bythe present invention. Referring to FIG. 3, the upper and side surfacesof a PGA 12 are covered with a resin protective cover 13, and contactpins 7 and stand pins 9 extend downwardly from the lower surface of thePGA 12. FIG. 4 is a sectional view of the PGA taken along the line 4--4of FIG. 3, and FIG. 5 is a bottom view of the PGA.

FIG. 6 is a sectional view of a PGA before molding. The same referencenumerals as in FIG. 1 denote the same constituent portions in FIG. 6. Ina PGA 14 before molding, an IC chip 4 is mounted on the upper surface ofa resin board 1 and connected to a terminal pattern 5 formed on theupper surface of the board 1 through lead wires 6. A plurality ofcontact pins 7 and stand pins 9 extend downwardly from the lower surfaceof the resin board 1. Inside the resin board 1, the contact pins 7 areelectrically connected to the terminal pattern 5 formed on the uppersurface of the resin board 1.

A lower mold 20 used in the present invention has a recess 21 at itscentral portion and a molding resin injection gate 22 in its uppersurface, as shown in FIG. 7. The bottom of the recess 21 serves as aflat support base 23 for supporting the PGA. Grooves 24 are formedaround the support base 23 for receiving the contact and stand pins 7and 9. The outer edge of the grooves 24 forms a flat support edge 25 forsupporting the PGA. Pairs of guide projections 27a, 27b, 27c, and 27dproject inwardly from the inner side wall surfaces 26 defining therecess 21 in the vicinity of the corners of the recess 21. When the PGA14 before molding is placed in the recess 21, the pairs of projectionsabut against the side surfaces of the PGA 14 at the four corners of theresin board 1 and prevent the PGA 14 from moving in the horizontaldirection.

When the PGA is to be molded, the PGA 14 as shown in FIG. 6, wherein theIC chip 4 is mounted on the resin board 1, is prepared. The PGA 14 isinserted under pressure in the recess 21 of the lower mold 20 fromabove. The PGA 14 is placed in the recess 21 such that the upper surfaceof the IC chip 4 is at a level slightly lower than the upper surface ofthe lower mold 20. The projections 27a, 27b, 27c, and 27d abut againstthe side surfaces of the four corners of the resin board 1 to positionthe board 1. The contact and stand pins 7 and 9 are received in thegrooves 24.

An upper mold 30 is positioned on the lower mold 20. The upper mold 30has a flat lower surface, as is seen in FIG. 7. In this state, betweenthe upper and lower molds 20 and 30, a gap G is formed on the upper andside surfaces of the PGA 14.

Subsequently, a thermosetting resin such as an epoxy resin containing aglass filler is pressurized and injected into the gap G through the gate22. The resin in the gap G is cured to mold the IC chip 4. Then, theupper mold 30 is lifted to release the PGA 14 and an excessive resin inthe gate 22 is cut off, thereby providing a PGA 12 molded by the resinprotective cover 13, as shown in FIG. 3.

As is seen from FIG. 3, in the PGA 12 obtained by the present invention,the upper and side surfaces of the resin board 1 including the IC chip 4are covered by the resin protective cover 13. Therefore, moisturepenetration from the cut side surfaces, as well as the upper surface, ofthe resin board 1 can be completely prevented, and no adverse effectacts on the IC chip and the wiring pattern as well, thereby increasingthe reliability of the product. Since resin molding is performed bytransfer molding that accompanies compression, a molded resin layerbecomes more dense than that obtained by a potting technique used inconventional resin molding, thus providing high moisture resistance.Since the PGA is inserted under pressure and fixed in the lower mold atthe time of resin molding, when a molding resin is injected from thegate, the PGA will not be undesirably moved by the injection pressure,and the product yield is increased.

FIG. 9 shows another example of the lower mold used in the presentinvention.

In this example, in place of the projections of the lower mold shown inFIG. 7, pairs of pins 28a, 28b, 28c, and 28d are formed at portions of asupport edge 25 that corresponds to the corners of a resin board 1 of aPGA. When the PGA is inserted under pressure in a recess 21 from above,the side surfaces of the four corners of the resin board 1 are abuttedagainst these pins and the board 1 is thus positioned. Excluding thispoint, the lower mold shown in FIG. 9 is the same as that shown in FIG.7 and a detailed description thereof is omitted.

In either lower mold described above, the projections or pins forpositioning the resin board of a PGA are provided at positionscorresponding to the four corners of the resin board. However, they maybe provided to correspond to only two diagonal corners or at a positionwhere they abut against any portion of a side of a resin board. Theprojections or pins may be of any shape.

FIG. 10 shows another upper mold used in the present invention.

A recess 30a slightly larger than an IC chip 4 of a PGA before molding,which is to be inserted in the recess 21 of the lower mold 20, is formedin the lower surface of an upper mold 30.

When the upper mold 30 is used in combination with the lower mold 20shown in FIG. 7 to form a protective cover of the PGA, a protectivecover 13 having a central projection 13a is formed, as shown in FIG. 11.The same reference numerals as in FIG. 3 denote the same constituentportions in FIG. 11.

In this manner, when the thickness of the central portion of theprotective cover 13 of the PGA is increased, a stronger protection forthe IC chip 4 can be expected, and weathering resistance and mechanicalstrength can be increased. If an upper mold having a flat lower surface,as shown in FIG. 7, is used, and when a thermosetting resin is injectedin the formation of a protective cover, the resin tends to flow in theperiphery of the PGA and the thickness of the resin on the centralportion of the upper surface of the PGA tends to be small. However, whenthe upper mold 30 as shown in FIG. 10 is used, such a problem can besolved.

What is claimed is:
 1. A pin grid array package comprising:a resinousprinted circuit board having an upper surface and a lower surface; asemiconductor chip mounted directly on the upper surface of the resinousprinted circuit board; a plurality of contact pins on the lower surfaceof the circuit board; a protective cover being transfer-molded andformed of a thermosetting resin; wherein the entire upper surface of theprinted circuit board, including the semiconductor chip, and sidesurfaces of the circuit board, are encapsulated by the protective cover.2. A pin grid array package comprising:a resinous printed circuit boardhaving an upper surface and a lower surface; a semiconductor chipmounted on the upper surface of the resinous printed circuit board; aplurality of contact pins on the lower surface of the circuit board; aprotective cover being transfer-molded, formed of a thermosetting resinand including recesses around the peripheral edges of a lower surfacethereof; wherein the entire upper surface of the printed circuit board,including the semiconductor chip, and side surfaces of the circuitboard, are encapsulated by the protective cover.
 3. A pin grid arraypackage comprising:a resinous printed circuit board having an uppersurface and a lower surface; a semiconductor mounted on the uppersurface of the resinous printed circuit board; a plurality of contactpins on the lower surface of the circuit board; a protective cover beingtransfer-molded, formed of a thermosetting resin and including athickened portion overlying the semiconductor chip; wherein the entireupper surface of the printed circuit board, including the semiconductorchip, and side surfaces of the circuit board, are encapsulated by theprotective cover.